CHANG-ES VIII: Uncovering Hidden AGN Activity in Radio Polarization

TL;DR

This study uses radio polarization observations to reveal hidden AGN activity in NGC 2992, showing bipolar outflows only visible in polarized emission, which helps uncover obscured nuclear activity in galaxies.

Contribution

First clear example of bipolar radio outflow detected solely through polarized emission, demonstrating a new method to uncover hidden AGN activity obscured in total intensity.

Findings

Polarized radio lobes are present without total intensity counterparts.

Radio lobes are interacting with the interstellar medium.

Polarization reveals hidden AGN activity obscured in other wavelengths.

Abstract

We report on C-band (5 - 7 GHz) observations of the galaxy, NGC~2992, from the CHANG-ES sample. This galaxy displays an embedded nuclear double-lobed radio morphology within its spiral disk, as revealed in linearly polarized emission but {\it not} in total intensity emission. The radio lobes are kpc-sized, similar to what has been observed in the past for other Seyfert galaxies, and show ordered magnetic fields. NGC~2992 has shown previous evidence for AGN-related activity, but not the linearly polarized radio features that we present here. We draw attention to this galaxy as the first clear example (and prototype) of bipolar radio outflow that is revealed in linearly polarized emission only. Such polarization observations, which are unobscured by dust, provide a new tool for uncovering hidden weak AGN activity which may otherwise be masked by brighter unpolarized emission within which it is embedded. The radio lobes observed in NGC~2992 are interacting with the surrounding interstellar medium and offer new opportunities to investigate the interactions between nuclear outflows and the ISM in nearby galaxies. We also compare the radio emission with a new CHANDRA X-ray image of this galaxy. A new CHANG-ES image of NGC~3079 is also briefly shown as another example as to how much more obvious radio lobes appear in linear polarization as opposed to total intensity.